Carburetor



PatentcdlSept. 24, 1940` UNITED STATESv PATENT, oFFcE a corporation of Indiana f Appui-,anun september z, 1937, semi no. 162,072

, 5 Claims. This invention relates to carburetors, and more particularlyA to downdraft Acarburetors of the` plain tube type generally adapted for automo tive vehicle internal combustion engine use.

In carburetors of the above general type two fuel discharge systems are usually employed, one 4being a 'main fuel nozzle and the other an idling nozzle, and provision is made for transferring from the operation of one nozzle to the other as the throttle is opened. Both nozzles may be of the air Vbled type, and to assist in a smooth transfer from one to the'othejr both nozzles may be supplied from a single well communicating with y fuel supply or float chamber, `so that the fuel ,mayl divide between the nozzles, depending on demand. During open throttle operation, particularly at low speed, it has been found that the usual' air bleed for the idling nozzle interferes ,with the operation of the main fuel nozzle, by supplying the same with excessair, thusY leaning out the mixture at a'time when increased power is 'especially desired andan enriched 4mixture would be preferablei if any change at all must take place. Such interference also empties the passages leading to' the idling nozzle, so that l upon a subsequent transfer Vback to the idling `mixture results. due to the to back bleed" to the nozzle. Under vcer-V nozzle, a momentary delay inthe supply of fuel time taken to restore fuel to these passages.

' In the pastA the air bleed for the idling nozzle has in general'been from a region of substanltially atmospheric' pressure such as the air horn between the choke valve and the venturi, and thus there was no resistance to the inflow of air 't any time when the idling nozzle or its'connesting passag were subjected to reduced pressure.

Under what may bel termed normal operating conditions, a sumcient pressure differential existsl between the idling nomic and the idling air `bleed inlet so that all of the air which enters the inlet is drawn o ut with the idling mixture at the idling nozzle, thus leaving no excessiair tain other operating conditions, however.. as at wide open throttle and mw engine speed, this differential is insuiiicient, with-the result'that part or all of the air enteringthe -idling bleed `port back b1 ether is, nu .drawn tothe main fuel `u`oz zle,- since suction on the idling nomic is too small in comparison with the suction on the main nomic in the Venturi 'l'o overcome this effect the present invention providesanidlingbleedinletintheinduction `polmzieatapointou!relativelylowsuction.

(c1. zel-41) between the venturi and throttle valve, so that with closed throttle the bleed inlet is exposed to substantially atmospheric pressure, `due to the relatively smallow through the intake, but the inlet is sodesigned that as thefrate of flow 5 through the induction passage increases,l the pressure at the bleed inlet` and the idling nozzle is decreasd, so ythat the decreasing pressure at the .main nozzle.``( due to Venturi depression, a function of the rate of air iiow therethrough). m does not produce back bleeding of air to the 'main nozzle: To accomplish this result, the bleed inlet may be made in the form of a, tube projecting into the air stream in the vicinity ofthe throttle. ,By modifying the 'shape and pou sition of the tube, varying degrees of' suction from the aix-.sweeping past it may be made effective upon the idling passages. Instead of projecting into the vicinity of the throttle, the

- inlet tube may be-connected into one of the -fuel-air ratio may be maintained throughout the n i entire range of speed and throttle opening variations. Accordingly an object of the invention is to provide a combined air bled idling and main fuel nozzle system `wherein back flow of air s from the bleed inlet for one nozzle cannot interfere with and lean out the mixture supplied by the -other nozzle. Another object .of the invention is to provide in a carburetor 'of the type described a system wherein the idling passages are not emptied fuel during the operation of the carburetor.

A further object of the invention is to provideV in a carburetor of the type described a bleedinlet for the idling nozzle sopositioned as to be under atmospheric pressure during closed throttle but subjected to subatmospheric pressure under certain conditions of operation.

Other objects of the invention have to do with providing a carburetor of improved characterisu ties` particularly with respectlto economy of operation throughout the range -of operations of Y theintemal combustion engine for which it is 'nie above and other novel'reames er the g invention will appear more fully hereinafter. from the following detailed description when taken in conjunction with the accompanying drawing.A It is expressly understood, however, that the drawing is employed for purpOses of illustration only and is not designed as a definition -of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawing, wherein likeA reference numerals indicate like parts:

Figure 1 is a longitudinal section through a carburetor embodying the hereinbefore described bleed principle; and

Figure 2,is a fragmentary section of a slightly modified 'form of Figure 1. I

Referring to Figurel 1, there is shown therein a carburetor of the plain tube downdraft type having an air horn l0, throttle valve I2, throttle body I4, large venturi I6, small venturi I3, fuel nozzle 20, and an idlingnozzle comprising discharge holes 22 and 23.

The main fuel 'nozzle is supplied with fuel frm a well 24 in communication with oat chamber 26 through a metering orice 25, the nozzle being air bled through a calibrated orifice 30 and a chamber 28 which connects with .the nozzle through port 32 at about the normal fuel level. The idling nozzle is connected to the well 24 through passages 33, 34, and 35, which together form an inverted U tube. Since the U tube is ln the form of a siphon, a break to atmosphere in the form of a. very small port 40 is providedy adapted to feed air into the lower end of tube 35,

to mix with the fuel which is thereafter drawn into the manifold through the adjustable discharge port 22.

To bleed the idling fuel with air prior to the introduction of air from the port 23 an air inlet 46 connecting the mixing chamber with the passage 35 is provided. When the throttle is closed, the movement of air through the induction passage is slow, so that the air inlet 46 is under atmospheric pressure and air is free to flow therethrough into the passage 35 to bleed the fuel.

In order to adapt port 46 to'function as an auxiliary nozzle under certain conditions, and to increase the suction effect thereon under all conditions, the port 46 is preferably provided with a tube 50 which projects into the induction passage and has a beveled inlet designed to produce a Pitot or negative impact effect to thus take advantage of the iiow velocity therepast to create additional suction. As shown in Figures 1 and 2, the inlet of tube 50 faces in the direction of air flow, but it`may if desired be rotated to obtain any degree of positive or negative impact effect, as may be, found desirable in the carburetor in which the invention is to be embodied.

As the throttle is opened, the port 23 is subjected to increasing suction transmitted from the intake manifold, so that fuel is discharged theretain a propel' mixture.

lgradually increases from 13 to 20 inches.

wider, the idling port 22, port 23, and tube 50 all become subjected to subatmospheric pressure of such degree that there can be no reverse flow of air up the passage 35 and into the base of the fuel well 24 to cause back bleeding of the main nozzle.

As the throttle is opened further and reaches the .position indicated at I2a in Figure. 1, the

vvacuum existing posterior to the throttle becomes fuel passage 35 located between the port 4B and the idling nozzle. Without this restriction, however, the throttle is closed suiiiciently to produce vacuum of from 13 to 20 inches of mercury on the idling nozzle, 'the flow remains a constant maximum, since any increase from about 13 inches does not increase the iiow of fuel. However, with the restriction, maximum flow doe's not occur at 13 inches, but with proper design can be made to gradually increase to maximum as the vacuum it is possible to provide a gradual increase or decrease in the discharge of idling fuel as the throttle is opened and closed, which results in considerable economy during closed or substantially closed throttle operation. The restriction also tends to cut down back bleeding from ports 22 and 23 to the port 46, when the latter is discharging fuel as above explained, and assists in maintaining fuel in the passage 35-immediately adjacentthe idling nozzle.L

While` several embodiments of the invention have been shown and described, they are merely by Way of illustrating the underlying principles. As many changes in construction and arrangement of parts and passageways may be made, without departing from thespirit of the invention, as will be-readily understood by those skilled L in the art, reference will be had to the appended claims for a denition of the invention.

What is claimed is:

1. In a carburetor of'the'plain tube downdraft type, an induction passage including a venturi and a throttle, a fuel chamber, a main fuel passage extending from said fuel chamber to the throat of said venturi, a main metering restriction -in the fuel passage, an idlingfuel passage leading from the main fuel passage posterior to passage adjacent the edge of the 'throttle when in closed position, an idle fuel metering restriction in theidle fuel passage, and a conduit leading from the idling fuel passage posterior to the metering restriction therein including a tube proand disposed as to be subject to a degree of suction increasing with the rate of such air flow.`

2. The invention defined in claim 1, wherein the outlet of the last mentioned conduit is positioned below -the normal level of fuel in the fuel chamber vand discharges fuel from the idling fuel 4passage into the induction passage due to increase'r of suction when the throttle is opened a predetermined amount.

-3. In a-carburetor of the plain tube downdraft Thus Athe main metering restriction to the induction,

`.'ecting into the induction passage between the venturi and the throttle and having its outlet facing in the direction of air flow andso formed induction passage, a throttle controlling duction passage adjacent the throttle, an idle fuel metering restriction in the passageway, a restricted air bleed into said passageway at a point above the fuel level in the fuel chamber and posterior to said idle fuel metering restriction, and a conduit leading from the passageway posterior to the restricted air bleed including a tube projecting into the induction passage betweenthe throttle and the venturi and having an outlet facing in the direction of air ow and positioned below the normal level of the fuel in the fuel chamber.

Il. In a plain tube carburetor comprising a main body portion and a throttle body portion, an in'- 25 duction passage extending through said portions,

a venturi in the main body portion of said induction-passage, a fuel chamben'a main fuel duct leading from said` chamber to the venturi and having a fuel metering, restriction therein, a throttle in the throttle vbody portion for controlling flow through the induction passage, an idle fuel nozzle discharging in the induction passage posterior to the throttle, n idling fuel duct comprising an inverted U-sh pecl passage having its upper portion above the normal level of fuel in the fuel chamber and having one of its vertical legsy communicating with the main fuel duct posterior to the restriction and the other leg l communicating with the idle fuel nozzle, and an idle air bleed nozzleprojecting into the throttle body portion connecting said lother leg with the induction passage between the throttle and the venturi, the entrance of said bleed nozzle opening Vin the direction of air flow to increase the suction thereon as the air flow increases.

5. The invention defined in claim 4 including a restriction in said other leg intermediate the air bleed and the idle fuel nozzle.

o. WIRTH. es 

